Remove std::string histogram name from HistogramBase object.

base/metrics/sparse_histogram_unittest.cc

Index: base/metrics/sparse_histogram_unittest.cc
diff --git a/base/metrics/sparse_histogram_unittest.cc b/base/metrics/sparse_histogram_unittest.cc
index 3ad2bc86801c05111c2354224bef2100eabaffc1..12517c16ff589a8803de88c32394191ca5e79240 100644
--- a/base/metrics/sparse_histogram_unittest.cc
+++ b/base/metrics/sparse_histogram_unittest.cc
@@ -73,7 +73,7 @@ class SparseHistogramTest : public testing::TestWithParam<bool> {
     GlobalHistogramAllocator::ReleaseForTesting();
   }
 
-  std::unique_ptr<SparseHistogram> NewSparseHistogram(const std::string& name) {
+  std::unique_ptr<SparseHistogram> NewSparseHistogram(const char* name) {
     return std::unique_ptr<SparseHistogram>(new SparseHistogram(name));
   }
 
@@ -181,7 +181,7 @@ TEST_P(SparseHistogramTest, MacroBasicTest) {
   HistogramBase* sparse_histogram = histograms[0];
 
   EXPECT_EQ(SPARSE_HISTOGRAM, sparse_histogram->GetHistogramType());
-  EXPECT_EQ("Sparse", sparse_histogram->histogram_name());
+  EXPECT_EQ("Sparse", StringPiece(sparse_histogram->histogram_name()));
   EXPECT_EQ(
       HistogramBase::kUmaTargetedHistogramFlag |
           (use_persistent_histogram_allocator_ ? HistogramBase::kIsPersistent